Field
The present invention provides for improved bonding compositions where the bonding composition includes a film former component. In particular, the present invention provides for improved bonding compositions useful in bonding polymers to substrates such as metals, glass or other hydroxylated substrates and in particular elastomer to substrate bonding compositions. Of particular interest are compositions comprising at least one non-halogenated polymer. The compositions of the invention display good bonding properties under various testing conditions, such as initial and pre-bakes tests. Such properties are of particular interest in vulcanisation processes.
Brief Description of Related Technology
Reinforced composite materials play a critical role in the manufacture of high-performance products that need to be lightweight, yet strong enough to take harsh loading and operating conditions. Popular reinforcing materials included wood, glass, metals, quartz and carbon fibres. Composites reinforced with these types of substrate may find utility in the manufacture of a number of structural materials such as aerospace components and racing car bodies.
Polymer to metal substrate and, in particular rubber, to metal bonding has been practised for many years. There are many applications for formulations which achieve polymer or rubber to metal bonding. Rubber to metal bonding is widely used to bond different metals to a natural or synthetic rubber so as to combine the structural strength of the metal with the elastomeric properties of the rubber.
Accordingly, metal and polymers such as rubber are often bonded to each other for impact absorption applications, such as in bearings, wheels, shock absorbers, moving arms, etc. Such components can be utilised on a very small scale, for example in PC components or on a very large scale for example in constructions such as bridges and buildings. Noise reduction may also be achieved by utilising metal to rubber bonding. It is accepted that tremendous forces can be experienced by any component that comprises metal and rubber bonded together. Thus, it is desirable to provide metal to rubber bonding, which can withstand significant forces, such as compressive or extensive pressures including shocks without having the metal or the rubber separate from each other. There are many other rubber to metal bonding applications, including tyre production where internal wire reinforcements for the tyre are bonded to the rubber of the tyre. Prior art compositions are discussed below.
Glass fibre reinforced composite materials consist of high strength glass fibres embedded in a matrix. For example, Glass Fibre Reinforced Concrete comprises glass fibres embedded in cement-based matrix and may find utility in buildings and other structural edifices. Similarly, Glass Reinforced Plastic comprises glass fibres embedded in a plastic material. Glass Reinforced Plastics are immensely versatile materials which combine to provide lightweight materials with high strength performance. Glass reinforced plastics find utility in a number of different areas from structural engineering to telecommunications.
Elastomer to glass bonding provides an attractive means by which the structural strength of glass can be combined with the elastomeric properties of the elastomer/rubber. Reinforcing fibres such as glass fibres have been used as a reinforcing material for rubber articles such as in rubber belts, tyres and hoses. In particular, glass fibres have been employed to reinforce automotive timing belts, where there is a need for synchronous transfer of power from crankshaft to overhead camshaft without loss of inertia.
Traditionally, such glass cord composites are manufactured by coating individual filaments of glass yarn with specialised coatings, such as resorcinol formaldehyde latex (“RFL”) formulations. Conventional rubber to metal bonding products are then employed to bond the RFL latex to the rubber via a vulcanisation step.
Traditional rubber-to-metal bonding technology incorporates a two-step system, where in a first step a primer is applied and thereafter in a second step an improved curable, for example, adhesive composition is applied. The primer ordinarily consists of solutions or suspensions of chlorinated rubber and phenolic resins containing reactive groups, and also pigments such as titanium dioxide, zinc oxide, carbon black, etc. The primer is generally applied as a thin layer onto a treated (cleaned) surface of a metallic component such as treated steel component for example a component that has been grit blasted or chemically treated.
The improved curable composition ordinarily consists of a large range of rubber materials and cross-linkers. These include, but are not restricted to, chlorinated and bromochlorinated rubbers, aromatic nitrosobenzene compounds and bismaleimide as cross-linkers, xylene, perchloroethylene and ethylbenzene as solvents, and also some lead or zinc salts. The improved curable composition layer is generally the link between the primed metal and the rubber. Other cross-linkers that have been employed in rubber-to-metal bonding technology are aromatic nitroso compounds, such as p-dinitrosobenzene.
Many formulations for rubber to metal bonding exist. For example silanes have been used as corrosion inhibitors and as rubber-to-metal bonding adhesion promoters. U.S. Patent Application Publication No. 2009/0181248 discloses substantially hydrolysed silane solutions, for example bis(trimethoxypropyl)amine and bis(triethoxypropyl)tetrasulfide, for use in a rubber to metal bonding composition. The amino silane and sulphide silane are formulated in a ratio of 1:3 respectively, in an ethanol/water solution.
International Patent Publication No. WO2004/078867 to Lord Corporation describes a single coat solvent-based improved curable composition designed to bond thermoplastic elastomers containing an alkoxy silane/urethane adduct and a chlorinated polymer. Methods of synthesis and formulation are described within this patent document. U.S. Pat. No. 4,031,120 to Lord Corporation describes a composition comprising an isocyanate functional organosilane, in combination with a polyisocyanate and an aromatic nitroso compound. The resulting system is described as a one-coat improved curable composition for bonding a variety of elastomeric materials to metals and other substrates.
Canadian Patent No. 1,087,774 describes a composition for use in the production of composite rubber materials. The composition discloses a one-part composition comprising a vulcanisable polymer, a discrete aromatic nitroso compound and a discrete organic phosphonic acids (and partial esters thereof). Problematically, the toxic nitrosobenzene component is freely formulated within the composition.
Generally, it is desirable that bonding is achieved during a vulcanisation step like compression moulding, transfer moulding, injection moulding and autoclave heating, for example with steam or hot air. For example, semi-solid rubber can be injected into a mould. The semi-solid rubber is then cross-linked into a fully cured rubber and the bond with the substrate is formed at the same time.
Certain requirements of the curing system are desirable. These include, ease of processing, stability (for example avoiding sedimentation), ease of application, fast drying (to allow handling without fouling), good wetting properties, and good curing strengths. Curing should be achieved independently of the type of elastomer (rubber) employed and also independently of the type of substrate. It will be appreciated that some rubbers are blended materials and accordingly it is desirable that good curing is achieved with such blended materials. Suitably consistent curing is achieved under various process parameters.
Certain elastomer to substrate adhesive compositions have typically comprised a film former component. Often the film former component includes a halogenated polymer (such as chlorinated isoprene, bromo/chloro butadiene) and a crosslinking agent (such as dinitrosobenzene or nitrososilane). The purpose of the film former is to allow the bonding composition to be applied (by spraying, rolling or dipping from solvent based adhesive composition) to the bonding substrate (usually a metal) as a dry tack free film. The coated part can then be bonded immediately or more usually after a desired period of time which conveniently allows for transportation to different facilities or allows for storage before bonding is carried out. The applied film needs to be robust and withstand typical chipping or scratching which can occur during transport or storage. The film former component should also not full react or cross-link too quickly at the vulcanisation temperature, otherwise poor bonding may occur (as evidenced by short pre-bake resistance, where the films react too quickly giving poor bonding). The film also needs be robust enough to resist being swept from the metal surface (sweep resistance) during for example, a rubber injection vulcanisation process. Therefore, the film must remain solid and have sweep resistance at the vulcanisation temperatures (normally 150-180° C.). The film former must not be so cross-linked or solid at the vulcanisation temperatures as to restrict the mobility or reactivity of nitroso moieties within with the rubber, otherwise poor bonding will result.
Notwithstanding the state of the art it would be desirable to provide improved compositions to bond polymeric substrates to a variety of substrates (such as metals, glass, quartz, etc.) that remedy some or all of the known deficiencies and/or provide alternatives to the existing technologies so that consumers have more possibilities from which to choose.